1. Field of the Invention
The present invention relates to a method for manufacturing a solid electrolytic capacitor with high performance and high reliability, by applying a solution of a. functional polymer composition useful as a solid electrolyte, and a rolled aluminum device.
2. Description of the Prior Art
Usually, a solid electrolytic capacitor has a structure comprising an electrode of metals, such as aluminum (Al) or tantalum (Ta), acting as an anode; an oxide film formed thereon via chemical treatment, as a dielectric layer; and a solid electrolyte-attached conductive layer of substances including graphite or silver formed on the, dielectric layer, as a part of a cathode. In this case as the solid electrolyte, use may be made of metal oxides such as manganese dioxide and lead oxide, TCNQ (7,7xe2x80x2,8,8xe2x80x2-tetracyanoquinodimethane) complex, which is an organic semiconductor, and polypyrrole, which is a conductive polymer.
Though generally used in tantalum (Ta) electrolytic capacitors, manganese dioxide can be applied to aluminum electrolytic capacitors, but with significant difficulty. Commonly, the impregnation of manganese dioxide into capacitors is carried out by immersing the capacitor device in manganese acetate solution, followed by performing a thermal decomposition therein. As a solid electrolyte, manganese dioxide is usually attached to an electrode. But, in the case of aluminum (Al) electrolytic capacitor, such thermal decomposition impairs a dielectric aluminum oxide film with concurrent drastic decrease in pressure resistance.
On the other hand, impregnation methods of TCNQ complex used in organic semiconductor devices utilize a dissolution-impregnation using heat, in which TCNQ complex is liquefied by heat and the devices are immersed in the liquefied TCNQ complex for impregnation. However, TCNQ complex is poorly resistant to heat. In particular, TCNQ complex suitable for the dissolution-impregnation should have a dissolution point of 270xc2x0 C. or lower owing to its decomposition point being about 290xc2x0 C., but this temperature is too low to provide resistance to soldering.
Recently, the development of new materials in the field of polymers has made considerable progress. As a result, conductive polymers comprising conjugated polymers doped with an electron-donating or electron-attracting compound (dopant) have been developed, which have stronger heat resistance than TCNQ complex, better electric conductivity than manganese dioxide and TCNQ complex, and low ESR (equivalent series radiation) of capacitor and impedance in a high frequency region. Among the developed polymers is polypyrrole. Polypyrrole, a functional polymer having heat resistance and good conductivity, is also used as a solid electrolyte. However, the impregnation of polypyrrole causes the pressure resistance of dielectric oxide film to be greatly lowered, as in manganese dioxide. Additionally, the application range of polypyrrole is limited. For example, the electrode in the flat form can be impregnated with polypyrrole, whereas the rolled form is very difficult to impregnate with polypyrrole.
It is an object of the present invention to alleviate said problems of the prior arts and to provide a method for preparing an organic semiconductor solid electrolytic capacitor which has high capacity, and low ESR and impedance in a high frequency region, by impregnating an aluminum electrode thin film-rolled device with a conductive polymer useful as a solid electrolyte.
In an aspect of the present invention, there is provided a method for manufacturing a solid electrolytic capacitor using a functional polymer, which comprises: rolling electrode lead-attached thin films of an etched aluminum and a cathode, together with a separator paper, to make a rolled device (S1); mixing an admixture of polyaniline Emeraldine base powder (1.0-5.0 wt %) and a dopant in a molar ratio of 1:2, pulverized by use of a rod mill or a ball mill, with a solution of 0.2-0.6 wt % of surfactant in equimolar amounts of a first solvent and a second solvent, and dissolving the pulverized mixture with stirring by use of a dissolution apparatus, to prepare a solution of a conductive polyaniline solid electrolyte (S2); and immersing said rolled device in said solution of conductive polyaniline solid electrolyte at a rate of 0.5-10 mm/sec, taking out the device from the solution at the same rate, and drying the device at 80-150xc2x0 C. for 5-30 minutes in a drying oven, followed by inserting the fully dried impregnated device to an aluminum can, to seal and cure the inserted device with epoxy resin, urethane or acryl resin (S3).
In another aspect of the present invention, there is provided a method for preparing a solid electrolytic capacitor using a functional polymer, which comprises; rolling electrode lead-attached thin films of an etched aluminum and a cathode, together with a separator paper, to make a rolled device (S1); mixing 2.0-20.0 wt % of a paste type solution of polyaniline Emeraldine base powder in dodecylbenzenesulfonic acid in a molar ratio of 1:4, pulverized by use of a rod mill or a 3 roll mill, with 69-91 wt % of a first solvent, and dissolving the pulverized mixture with stirring by use of a dissolution apparatus, followed by adding a second solvent in the amount corresponding to 10 wt % of the first solvent to decrease volatility of the solution, to prepare a precoating solution (S2); immersing said rolled device in said precoating solution at a rate of 0.5-10 mm/sec, taking out the device from the solution at the same rate, and drying the device at 50-100xc2x0 C. for 10 secondsxe2x80x945 minutes in a drying oven (S3); mixing an admixture of polyaniline Emeraldine base powder (1.0-5.0 wt %) and a dopant in a molar ratio of 1:2, pulverized by use of a rod mill or a ball mill, with a solution of 0.2-0.6 wt % of surfactant in equimolar amounts of a third solvent and a fourth solvent, and dissolving the pulverized mixture with stirring by use of a dissolution apparatus, to prepare a solution of a conductive polyaniline solid electrolyte (S4); and immersing the rolled device precoated at previous step (S3) in said solution of conductive polyaniline solid electrolyte at a rate of 0.5-10 mm/sec, taking out the device from the solution at the same rate, and drying the device at 80-150xc2x0 C. for 5-30 minutes in a drying oven, followed by inserting the fully dried impregnated device to an aluminum can, to seal and cure the inserted device with epoxy resin, urethane or acryl resin (S5).
As mentioned above, the electrode lead is attached to each of the aluminum etching thin film and the cathode thin film and then rolled, together with a separator paper, to prepare a rolled device, which is simply immersed in the solution of conductive polymer solid electrolyte at normal temperature and pressure, thereby forming a solid electrolyte layer with high impregnation efficiency. In consequence, the solid electrolytic capacitor which is advantageous in terms of easier impregnation, more excellent leakage current properties and larger electrostatic capacity, can be prepared according to the present invention, compared with conventional solid electrolytic capacitors.